I have a Mug that YouTube UK sent me after I completed a survey for them. It says "User Generated Coffee" on one side and has the YouTube logo on the other.
It's never been used
I think it is quite rare as google searches don't come up with much.
If I decided to put it on eBay how much would I likely get for it?
you would be likely to get however much someone was willing to pay for it i guess. You could put it on 1 week and noone will bid, or you could put it on another week and 2 people who want it might outbid each other